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23 .TH TCPDUMP 1 "8 August 2002"
25 tcpdump \- dump traffic on a network
30 .B \-aAdDeflnNOpqRStuvxX
85 \fITcpdump\fP prints out the headers of packets on a network interface
86 that match the boolean \fIexpression\fP. It can also be run with the
88 flag, which causes it to save the packet data to a file for later
89 analysis, and/or with the
91 flag, which causes it to read from a saved packet file rather than to
92 read packets from a network interface. In all cases, only packets that
99 will, if not run with the
101 flag, continue capturing packets until it is interrupted by a SIGINT
102 signal (generated, for example, by typing your interrupt character,
103 typically control-C) or a SIGTERM signal (typically generated with the
105 command); if run with the
107 flag, it will capture packets until it is interrupted by a SIGINT or
108 SIGTERM signal or the specified number of packets have been processed.
112 finishes capturing packets, it will report counts of:
114 packets ``received by filter'' (the meaning of this depends on the OS on
117 and possibly on the way the OS was configured - if a filter was
118 specified on the command line, on some OSes it counts packets regardless
119 of whether they were matched by the filter expression, and on other OSes
120 it counts only packets that were matched by the filter expression and
124 packets ``dropped by kernel'' (this is the number of packets that were
125 dropped, due to a lack of buffer space, by the packet capture mechanism
128 is running, if the OS reports that information to applications; if not,
129 it will be reported as 0).
131 On platforms that support the SIGINFO signal, such as most BSDs, it will
132 report those counts when it receives a SIGINFO signal (generated, for
133 example, by typing your ``status'' character, typically control-T) and
134 will continue capturing packets.
136 Reading packets from a network interface may require that you have
139 .B Under SunOS 3.x or 4.x with NIT or BPF:
140 You must have read access to
145 .B Under Solaris with DLPI:
146 You must have read/write access to the network pseudo device, e.g.
148 On at least some versions of Solaris, however, this is not sufficient to
151 to capture in promiscuous mode; on those versions of Solaris, you must
154 must be installed setuid to root, in order to capture in promiscuous
155 mode. Note that, on many (perhaps all) interfaces, if you don't capture
156 in promiscuous mode, you will not see any outgoing packets, so a capture
157 not done in promiscuous mode may not be very useful.
159 .B Under HP-UX with DLPI:
162 must be installed setuid to root.
164 .B Under IRIX with snoop:
167 must be installed setuid to root.
172 must be installed setuid to root.
174 .B Under Ultrix and Digital UNIX/Tru64 UNIX:
175 Any user may capture network traffic with
177 However, no user (not even the super-user) can capture in promiscuous
178 mode on an interface unless the super-user has enabled promiscuous-mode
179 operation on that interface using
181 and no user (not even the super-user) can capture unicast traffic
182 received by or sent by the machine on an interface unless the super-user
183 has enabled copy-all-mode operation on that interface using
187 packet capture on an interface probably requires that either
188 promiscuous-mode or copy-all-mode operation, or both modes of
189 operation, be enabled on that interface.
192 You must have read access to
195 Reading a saved packet file doesn't require special privileges.
200 Print each packet (minus its link level header) in ASCII. Handy for
204 Attempt to convert network and broadcast addresses to names.
207 Exit after receiving \fIcount\fP packets.
210 Before writing a raw packet to a savefile, check whether the file is
211 currently larger than \fIfile_size\fP and, if so, close the current
212 savefile and open a new one. Savefiles after the first savefile will
213 have the name specified with the
215 flag, with a number after it, starting at 2 and continuing upward.
216 The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes,
217 not 1,048,576 bytes).
220 Dump the compiled packet-matching code in a human readable form to
221 standard output and stop.
224 Dump packet-matching code as a
229 Dump packet-matching code as decimal numbers (preceded with a count).
232 Print the list of the network interfaces available on the system and on
235 can capture packets. For each network interface, a number and an
236 interface name, possibly followed by a text description of the
237 interface, is printed. The interface name or the number can be supplied
240 flag to specify an interface on which to capture.
242 This can be useful on systems that don't have a command to list them
243 (e.g., Windows systems, or UNIX systems lacking
244 .BR "ifconfig \-a" );
245 the number can be useful on Windows 2000 and later systems, where the
246 interface name is a somewhat complex string.
250 flag will not be supported if
252 was built with an older version of
255 .B pcap_findalldevs()
259 Print the link-level header on each dump line.
262 Use \fIalgo:secret\fP for decrypting IPsec ESP packets.
268 \fBcast128-cbc\fP, or
270 The default is \fBdes-cbc\fP.
271 The ability to decrypt packets is only present if \fItcpdump\fP was compiled
272 with cryptography enabled.
273 \fIsecret\fP the ASCII text for ESP secret key.
274 We cannot take arbitrary binary value at this moment.
275 The option assumes RFC2406 ESP, not RFC1827 ESP.
276 The option is only for debugging purposes, and
277 the use of this option with truly `secret' key is discouraged.
278 By presenting IPsec secret key onto command line
279 you make it visible to others, via
284 Print `foreign' IPv4 addresses numerically rather than symbolically
285 (this option is intended to get around serious brain damage in
286 Sun's NIS server \(em usually it hangs forever translating non-local
289 The test for `foreign' IPv4 addresses is done using the IPv4 address and
290 netmask of the interface on which capture is being done. If that
291 address or netmask are not available, available, either because the
292 interface on which capture is being done has no address or netmask or
293 because the capture is being done on the Linux "any" interface, which
294 can capture on more than one interface, this option will not work
298 Use \fIfile\fP as input for the filter expression.
299 An additional expression given on the command line is ignored.
302 Listen on \fIinterface\fP.
303 If unspecified, \fItcpdump\fP searches the system interface list for the
304 lowest numbered, configured up interface (excluding loopback).
305 Ties are broken by choosing the earliest match.
307 On Linux systems with 2.2 or later kernels, an
309 argument of ``any'' can be used to capture packets from all interfaces.
310 Note that captures on the ``any'' device will not be done in promiscuous
315 flag is supported, an interface number as printed by that flag can be
321 Make stdout line buffered.
322 Useful if you want to see the data
326 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
327 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
330 Load SMI MIB module definitions from file \fImodule\fR.
332 can be used several times to load several MIB modules into \fItcpdump\fP.
335 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
338 Don't print domain name qualification of host names.
340 if you give this flag then \fItcpdump\fP will print ``nic''
341 instead of ``nic.ddn.mil''.
344 Do not run the packet-matching code optimizer.
346 if you suspect a bug in the optimizer.
349 \fIDon't\fP put the interface
350 into promiscuous mode.
351 Note that the interface might be in promiscuous
352 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
353 `ether host {local-hw-addr} or ether broadcast'.
356 Quick (quiet?) output.
357 Print less protocol information so output
361 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
362 If specified, \fItcpdump\fP will not print replay prevention field.
363 Since there is no protocol version field in ESP/AH specification,
364 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
367 Read packets from \fIfile\fR (which was created with the -w option).
368 Standard input is used if \fIfile\fR is ``-''.
371 Print absolute, rather than relative, TCP sequence numbers.
374 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
375 default of 68 (with SunOS's NIT, the minimum is actually 96).
376 68 bytes is adequate for IP, ICMP, TCP
377 and UDP but may truncate protocol information from name server and NFS
379 Packets truncated because of a limited snapshot
380 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
381 is the name of the protocol level at which the truncation has occurred.
382 Note that taking larger snapshots both increases
383 the amount of time it takes to process packets and, effectively,
384 decreases the amount of packet buffering.
385 This may cause packets to be
387 You should limit \fIsnaplen\fP to the smallest number that will
388 capture the protocol information you're interested in.
390 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
393 Force packets selected by "\fIexpression\fP" to be interpreted the
394 specified \fItype\fR.
395 Currently known types are
396 \fBcnfp\fR (Cisco NetFlow protocol),
397 \fBrpc\fR (Remote Procedure Call),
398 \fBrtp\fR (Real-Time Applications protocol),
399 \fBrtcp\fR (Real-Time Applications control protocol),
400 \fBsnmp\fR (Simple Network Management Protocol),
401 \fBvat\fR (Visual Audio Tool),
403 \fBwb\fR (distributed White Board).
406 \fIDon't\fP print a timestamp on each dump line.
409 Print an unformatted timestamp on each dump line.
412 Print a delta (in micro-seconds) between current and previous line
416 Print a timestamp in default format proceeded by date on each dump line.
419 Print undecoded NFS handles.
422 (Slightly more) verbose output.
423 For example, the time to live,
424 identification, total length and options in an IP packet are printed.
425 Also enables additional packet integrity checks such as verifying the
426 IP and ICMP header checksum.
429 Even more verbose output.
430 For example, additional fields are
431 printed from NFS reply packets, and SMB packets are fully decoded.
434 Even more verbose output.
436 telnet \fBSB\fP ... \fBSE\fP options
440 telnet options are printed in hex as well.
443 Write the raw packets to \fIfile\fR rather than parsing and printing
445 They can later be printed with the \-r option.
446 Standard output is used if \fIfile\fR is ``-''.
449 Print each packet (minus its link level header, unless
453 The smaller of the entire packet or
455 bytes will be printed. Note that this is the entire link-layer
456 packet, so for link layers that pad (e.g. Ethernet), the padding bytes
457 will also be printed when the higher layer packet is shorter than the
461 When printing hex, print ASCII too.
464 is also set, the packet is printed in hex/ASCII.
465 This is very handy for analysing new protocols.
468 is not also set, some parts of some packets may be printed
470 .IP "\fI expression\fP"
472 selects which packets will be dumped.
473 If no \fIexpression\fP
474 is given, all packets on the net will be dumped.
476 only packets for which \fIexpression\fP is `true' will be dumped.
478 The \fIexpression\fP consists of one or more
480 Primitives usually consist of an
482 (name or number) preceded by one or more qualifiers.
484 different kinds of qualifier:
486 qualifiers say what kind of thing the id name or number refers to.
492 E.g., `host foo', `net 128.3', `port 20'.
498 qualifiers specify a particular transfer direction to and/or from
500 Possible directions are
507 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
509 there is no dir qualifier,
512 For `null' link layers (i.e. point to point protocols such as slip) the
516 qualifiers can be used to specify a desired direction.
518 qualifiers restrict the match to a particular protocol.
533 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
535 no proto qualifier, all protocols consistent with the type are
537 E.g., `src foo' means `(ip or arp or rarp) src foo'
538 (except the latter is not legal syntax), `net bar' means `(ip or
539 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
541 [`fddi' is actually an alias for `ether'; the parser treats them
542 identically as meaning ``the data link level used on the specified
543 network interface.'' FDDI headers contain Ethernet-like source
544 and destination addresses, and often contain Ethernet-like packet
545 types, so you can filter on these FDDI fields just as with the
546 analogous Ethernet fields.
547 FDDI headers also contain other fields,
548 but you cannot name them explicitly in a filter expression.
550 Similarly, `tr' and `wlan' are aliases for `ether'; the previous
551 paragraph's statements about FDDI headers also apply to Token Ring
552 and 802.11 wireless LAN headers. For 802.11 headers, the destination
553 address is the DA field and the source address is the SA field; the
554 BSSID, RA, and TA fields aren't tested.]
556 In addition to the above, there are some special `primitive' keywords
557 that don't follow the pattern:
562 and arithmetic expressions.
563 All of these are described below.
565 More complex filter expressions are built up by using the words
570 to combine primitives.
571 E.g., `host foo and not port ftp and not port ftp-data'.
572 To save typing, identical qualifier lists can be omitted.
574 `tcp dst port ftp or ftp-data or domain' is exactly the same as
575 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
577 Allowable primitives are:
578 .IP "\fBdst host \fIhost\fR"
579 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
580 which may be either an address or a name.
581 .IP "\fBsrc host \fIhost\fR"
582 True if the IPv4/v6 source field of the packet is \fIhost\fP.
583 .IP "\fBhost \fIhost\fP
584 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
585 Any of the above host expressions can be prepended with the keywords,
586 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
589 \fBip host \fIhost\fR
592 which is equivalent to:
595 \fBether proto \fI\\ip\fB and host \fIhost\fR
598 If \fIhost\fR is a name with multiple IP addresses, each address will
599 be checked for a match.
600 .IP "\fBether dst \fIehost\fP
601 True if the ethernet destination address is \fIehost\fP.
603 may be either a name from /etc/ethers or a number (see
606 .IP "\fBether src \fIehost\fP
607 True if the ethernet source address is \fIehost\fP.
608 .IP "\fBether host \fIehost\fP
609 True if either the ethernet source or destination address is \fIehost\fP.
610 .IP "\fBgateway\fP \fIhost\fP
611 True if the packet used \fIhost\fP as a gateway.
613 source or destination address was \fIhost\fP but neither the IP source
614 nor the IP destination was \fIhost\fP.
615 \fIHost\fP must be a name and
616 must be found both by the machine's host-name-to-IP-address resolution
617 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
618 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
619 (An equivalent expression is
622 \fBether host \fIehost \fBand not host \fIhost\fR
625 which can be used with either names or numbers for \fIhost / ehost\fP.)
626 This syntax does not work in IPv6-enabled configuration at this moment.
627 .IP "\fBdst net \fInet\fR"
628 True if the IPv4/v6 destination address of the packet has a network
630 \fINet\fP may be either a name from /etc/networks
631 or a network number (see \fInetworks(4)\fP for details).
632 .IP "\fBsrc net \fInet\fR"
633 True if the IPv4/v6 source address of the packet has a network
635 .IP "\fBnet \fInet\fR"
636 True if either the IPv4/v6 source or destination address of the packet has a network
638 .IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
639 True if the IP address matches \fInet\fR with the specific \fInetmask\fR.
640 May be qualified with \fBsrc\fR or \fBdst\fR.
641 Note that this syntax is not valid for IPv6 \fInet\fR.
642 .IP "\fBnet \fInet\fR/\fIlen\fR"
643 True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
645 May be qualified with \fBsrc\fR or \fBdst\fR.
646 .IP "\fBdst port \fIport\fR"
647 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
648 destination port value of \fIport\fP.
649 The \fIport\fP can be a number or a name used in /etc/services (see
653 If a name is used, both the port
654 number and protocol are checked.
655 If a number or ambiguous name is used,
656 only the port number is checked (e.g., \fBdst port 513\fR will print both
657 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
658 both tcp/domain and udp/domain traffic).
659 .IP "\fBsrc port \fIport\fR"
660 True if the packet has a source port value of \fIport\fP.
661 .IP "\fBport \fIport\fR"
662 True if either the source or destination port of the packet is \fIport\fP.
663 Any of the above port expressions can be prepended with the keywords,
664 \fBtcp\fP or \fBudp\fP, as in:
667 \fBtcp src port \fIport\fR
670 which matches only tcp packets whose source port is \fIport\fP.
671 .IP "\fBless \fIlength\fR"
672 True if the packet has a length less than or equal to \fIlength\fP.
673 This is equivalent to:
676 \fBlen <= \fIlength\fP.
679 .IP "\fBgreater \fIlength\fR"
680 True if the packet has a length greater than or equal to \fIlength\fP.
681 This is equivalent to:
684 \fBlen >= \fIlength\fP.
687 .IP "\fBip proto \fIprotocol\fR"
688 True if the packet is an IP packet (see
690 of protocol type \fIprotocol\fP.
691 \fIProtocol\fP can be a number or one of the names
692 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
693 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
694 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
695 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
696 Note that this primitive does not chase the protocol header chain.
697 .IP "\fBip6 proto \fIprotocol\fR"
698 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
699 Note that this primitive does not chase the protocol header chain.
700 .IP "\fBip6 protochain \fIprotocol\fR"
701 True if the packet is IPv6 packet,
702 and contains protocol header with type \fIprotocol\fR
703 in its protocol header chain.
707 \fBip6 protochain 6\fR
710 matches any IPv6 packet with TCP protocol header in the protocol header chain.
711 The packet may contain, for example,
712 authentication header, routing header, or hop-by-hop option header,
713 between IPv6 header and TCP header.
714 The BPF code emitted by this primitive is complex and
715 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
716 so this can be somewhat slow.
717 .IP "\fBip protochain \fIprotocol\fR"
718 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
719 .IP "\fBether broadcast\fR"
720 True if the packet is an ethernet broadcast packet.
723 .IP "\fBip broadcast\fR"
724 True if the packet is an IPv4 broadcast packet.
725 It checks for both the all-zeroes and all-ones broadcast conventions,
726 and looks up the subnet mask on the interface on which the capture is
729 If the subnet mask of the interface on which the capture is being done
730 is not available, either because the interface on which capture is being
731 done has no netmask or because the capture is being done on the Linux
732 "any" interface, which can capture on more than one interface, this
733 check will not work correctly.
734 .IP "\fBether multicast\fR"
735 True if the packet is an ethernet multicast packet.
738 This is shorthand for `\fBether[0] & 1 != 0\fP'.
739 .IP "\fBip multicast\fR"
740 True if the packet is an IP multicast packet.
741 .IP "\fBip6 multicast\fR"
742 True if the packet is an IPv6 multicast packet.
743 .IP "\fBether proto \fIprotocol\fR"
744 True if the packet is of ether type \fIprotocol\fR.
745 \fIProtocol\fP can be a number or one of the names
746 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
747 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
748 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
749 Note these identifiers are also keywords
750 and must be escaped via backslash (\\).
752 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), Token Ring
753 (e.g., `\fBtr protocol arp\fR'), and IEEE 802.11 wireless LANS (e.g.,
754 `\fBwlan protocol arp\fR'), for most of those protocols, the
755 protocol identification comes from the 802.2 Logical Link Control (LLC)
756 header, which is usually layered on top of the FDDI, Token Ring, or
759 When filtering for most protocol identifiers on FDDI, Token Ring, or
760 802.11, \fItcpdump\fR checks only the protocol ID field of an LLC header
761 in so-called SNAP format with an Organizational Unit Identifier (OUI) of
762 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
763 is in SNAP format with an OUI of 0x000000.
768 \fItcpdump\fR checks the DSAP (Destination Service Access Point) and
769 SSAP (Source Service Access Point) fields of the LLC header;
771 \fBstp\fP and \fInetbeui\fP
772 \fItcpdump\fR checks the DSAP of the LLC header;
775 \fItcpdump\fR checks for a SNAP-format packet with an OUI of 0x080007
776 and the Appletalk etype.
779 In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field
780 for most of those protocols. The exceptions are:
783 \fBiso\fP, \fBsap\fP, and \fBnetbeui\fP
784 \fItcpdump\fR checks for an 802.3 frame and then checks the LLC header as
785 it does for FDDI, Token Ring, and 802.11;
788 \fItcpdump\fR checks both for the Appletalk etype in an Ethernet frame and
789 for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11;
792 \fItcpdump\fR checks for the Appletalk ARP etype in either an Ethernet
793 frame or an 802.2 SNAP frame with an OUI of 0x000000;
796 \fItcpdump\fR checks for the IPX etype in an Ethernet frame, the IPX
797 DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of
798 IPX, and the IPX etype in a SNAP frame.
800 .IP "\fBdecnet src \fIhost\fR"
801 True if the DECNET source address is
803 which may be an address of the form ``10.123'', or a DECNET host
805 [DECNET host name support is only available on Ultrix systems
806 that are configured to run DECNET.]
807 .IP "\fBdecnet dst \fIhost\fR"
808 True if the DECNET destination address is
810 .IP "\fBdecnet host \fIhost\fR"
811 True if either the DECNET source or destination address is
813 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
817 \fBether proto \fIp\fR
820 where \fIp\fR is one of the above protocols.
821 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
825 \fBether proto \fIp\fR
828 where \fIp\fR is one of the above protocols.
830 \fItcpdump\fP does not currently know how to parse these protocols.
831 .IP "\fBvlan \fI[vlan_id]\fR"
832 True if the packet is an IEEE 802.1Q VLAN packet.
833 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
835 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
836 changes the decoding offsets for the remainder of \fIexpression\fR
837 on the assumption that the packet is a VLAN packet.
838 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
842 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
845 where \fIp\fR is one of the above protocols.
846 .IP "\fBiso proto \fIprotocol\fR"
847 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
848 \fIProtocol\fP can be a number or one of the names
849 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
850 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
857 where \fIp\fR is one of the above protocols.
858 .IP "\fBl1\fR, \fBl2\fR, \fBiih\fR, \fBlsp\fR, \fBsnp\fR, \fBcsnp\fR, \fBpsnp\fR"
859 Abbreviations for IS-IS PDU types.
860 .IP "\fBvpi\fP \fIn\fR
861 True if the packet is an ATM packet, for SunATM on Solaris, with a
862 virtual path identifier of
864 .IP "\fBvci\fP \fIn\fR
865 True if the packet is an ATM packet, for SunATM on Solaris, with a
866 virtual channel identifier of
869 True if the packet is an ATM packet, for SunATM on Solaris, and is
871 Note that the first \fBlane\fR keyword encountered in \fIexpression\fR
872 changes the tests done in the remainder of \fIexpression\fR
873 on the assumption that the packet is either a LANE emulated Ethernet
874 packet or a LANE LE Control packet. If \fBlane\fR isn't specified, the
875 tests are done under the assumption that the packet is an
876 LLC-encapsulated packet.
878 True if the packet is an ATM packet, for SunATM on Solaris, and is
879 an LLC-encapsulated packet.
881 True if the packet is an ATM packet, for SunATM on Solaris, and is
882 a segment OAM F4 flow cell (VPI=0 & VCI=3).
884 True if the packet is an ATM packet, for SunATM on Solaris, and is
885 an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
887 True if the packet is an ATM packet, for SunATM on Solaris, and is
888 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
890 True if the packet is an ATM packet, for SunATM on Solaris, and is
891 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
893 True if the packet is an ATM packet, for SunATM on Solaris, and is
894 on a meta signaling circuit (VPI=0 & VCI=1).
896 True if the packet is an ATM packet, for SunATM on Solaris, and is
897 on a broadcast signaling circuit (VPI=0 & VCI=2).
899 True if the packet is an ATM packet, for SunATM on Solaris, and is
900 on a signaling circuit (VPI=0 & VCI=5).
902 True if the packet is an ATM packet, for SunATM on Solaris, and is
903 on an ILMI circuit (VPI=0 & VCI=16).
905 True if the packet is an ATM packet, for SunATM on Solaris, and is
906 on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
907 Connect Ack, Release, or Release Done message.
908 .IP \fBmetaconnect\fP
909 True if the packet is an ATM packet, for SunATM on Solaris, and is
910 on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
911 Release, or Release Done message.
912 .IP "\fIexpr relop expr\fR"
913 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
914 and \fIexpr\fR is an arithmetic expression composed of integer constants
915 (expressed in standard C syntax), the normal binary operators
916 [+, -, *, /, &, |], a length operator, and special packet data accessors.
918 data inside the packet, use the following syntax:
921 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
924 \fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link,
925 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
926 indicates the protocol layer for the index operation.
927 (\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the
929 Note that \fItcp, udp\fR and other upper-layer protocol types only
930 apply to IPv4, not IPv6 (this will be fixed in the future).
931 The byte offset, relative to the indicated protocol layer, is
933 \fISize\fR is optional and indicates the number of bytes in the
934 field of interest; it can be either one, two, or four, and defaults to one.
935 The length operator, indicated by the keyword \fBlen\fP, gives the
936 length of the packet.
938 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
939 The expression `\fBip[0] & 0xf != 5\fP'
940 catches all IP packets with options.
942 `\fBip[6:2] & 0x1fff = 0\fP'
943 catches only unfragmented datagrams and frag zero of fragmented datagrams.
944 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
946 For instance, \fBtcp[0]\fP always means the first
947 byte of the TCP \fIheader\fP, and never means the first byte of an
948 intervening fragment.
950 Some offsets and field values may be expressed as names rather than
952 The following protocol header field offsets are
953 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
954 code field), and \fBtcpflags\fP (TCP flags field).
956 The following ICMP type field values are available: \fBicmp-echoreply\fP,
957 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
958 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
959 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
960 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
961 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
963 The following TCP flags field values are available: \fBtcp-fin\fP,
964 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP, \fBtcp-push\fP,
965 \fBtcp-ack\fP, \fBtcp-urg\fP.
967 Primitives may be combined using:
969 A parenthesized group of primitives and operators
970 (parentheses are special to the Shell and must be escaped).
972 Negation (`\fB!\fP' or `\fBnot\fP').
974 Concatenation (`\fB&&\fP' or `\fBand\fP').
976 Alternation (`\fB||\fP' or `\fBor\fP').
978 Negation has highest precedence.
979 Alternation and concatenation have equal precedence and associate
981 Note that explicit \fBand\fR tokens, not juxtaposition,
982 are now required for concatenation.
984 If an identifier is given without a keyword, the most recent keyword
989 \fBnot host vs and ace\fR
995 \fBnot host vs and host ace\fR
998 which should not be confused with
1001 \fBnot ( host vs or ace )\fR
1005 Expression arguments can be passed to \fItcpdump\fP as either a single
1006 argument or as multiple arguments, whichever is more convenient.
1007 Generally, if the expression contains Shell metacharacters, it is
1008 easier to pass it as a single, quoted argument.
1009 Multiple arguments are concatenated with spaces before being parsed.
1012 To print all packets arriving at or departing from \fIsundown\fP:
1015 \fBtcpdump host sundown\fP
1019 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
1022 \fBtcpdump host helios and \\( hot or ace \\)\fP
1026 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
1029 \fBtcpdump ip host ace and not helios\fP
1033 To print all traffic between local hosts and hosts at Berkeley:
1037 tcpdump net ucb-ether
1041 To print all ftp traffic through internet gateway \fIsnup\fP:
1042 (note that the expression is quoted to prevent the shell from
1043 (mis-)interpreting the parentheses):
1047 tcpdump 'gateway snup and (port ftp or ftp-data)'
1051 To print traffic neither sourced from nor destined for local hosts
1052 (if you gateway to one other net, this stuff should never make it
1053 onto your local net).
1057 tcpdump ip and not net \fIlocalnet\fP
1061 To print the start and end packets (the SYN and FIN packets) of each
1062 TCP conversation that involves a non-local host.
1066 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
1070 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
1074 tcpdump 'gateway snup and ip[2:2] > 576'
1078 To print IP broadcast or multicast packets that were
1080 sent via ethernet broadcast or multicast:
1084 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
1088 To print all ICMP packets that are not echo requests/replies (i.e., not
1093 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
1098 The output of \fItcpdump\fP is protocol dependent.
1100 gives a brief description and examples of most of the formats.
1108 If the '-e' option is given, the link level header is printed out.
1109 On ethernets, the source and destination addresses, protocol,
1110 and packet length are printed.
1112 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
1113 the `frame control' field, the source and destination addresses,
1114 and the packet length.
1115 (The `frame control' field governs the
1116 interpretation of the rest of the packet.
1117 Normal packets (such
1118 as those containing IP datagrams) are `async' packets, with a priority
1119 value between 0 and 7; for example, `\fBasync4\fR'.
1121 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
1122 the LLC header is printed if it is \fInot\fR an ISO datagram or a
1123 so-called SNAP packet.
1125 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
1126 the `access control' and `frame control' fields, the source and
1127 destination addresses, and the packet length.
1128 As on FDDI networks,
1129 packets are assumed to contain an LLC packet.
1130 Regardless of whether
1131 the '-e' option is specified or not, the source routing information is
1132 printed for source-routed packets.
1134 On 802.11 networks, the '-e' option causes \fItcpdump\fP to print
1135 the `frame control' fields, all of the addresses in the 802.11 header,
1136 and the packet length.
1137 As on FDDI networks,
1138 packets are assumed to contain an LLC packet.
1140 \fI(N.B.: The following description assumes familiarity with
1141 the SLIP compression algorithm described in RFC-1144.)\fP
1143 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
1144 packet type, and compression information are printed out.
1145 The packet type is printed first.
1146 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
1147 No further link information is printed for \fIip\fR packets.
1148 For TCP packets, the connection identifier is printed following the type.
1149 If the packet is compressed, its encoded header is printed out.
1150 The special cases are printed out as
1151 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
1152 the sequence number (or sequence number and ack) has changed.
1153 If it is not a special case,
1154 zero or more changes are printed.
1155 A change is indicated by U (urgent pointer), W (window), A (ack),
1156 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
1157 or a new value (=n).
1158 Finally, the amount of data in the packet and compressed header length
1161 For example, the following line shows an outbound compressed TCP packet,
1162 with an implicit connection identifier; the ack has changed by 6,
1163 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
1164 data and 6 bytes of compressed header:
1167 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
1173 Arp/rarp output shows the type of request and its arguments.
1175 format is intended to be self explanatory.
1176 Here is a short sample taken from the start of an `rlogin' from
1177 host \fIrtsg\fP to host \fIcsam\fP:
1181 \f(CWarp who-has csam tell rtsg
1182 arp reply csam is-at CSAM\fR
1186 The first line says that rtsg sent an arp packet asking
1187 for the ethernet address of internet host csam.
1189 replies with its ethernet address (in this example, ethernet addresses
1190 are in caps and internet addresses in lower case).
1192 This would look less redundant if we had done \fItcpdump \-n\fP:
1196 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
1197 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
1201 If we had done \fItcpdump \-e\fP, the fact that the first packet is
1202 broadcast and the second is point-to-point would be visible:
1206 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
1207 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
1211 For the first packet this says the ethernet source address is RTSG, the
1212 destination is the ethernet broadcast address, the type field
1213 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
1217 \fI(N.B.:The following description assumes familiarity with
1218 the TCP protocol described in RFC-793.
1219 If you are not familiar
1220 with the protocol, neither this description nor \fItcpdump\fP will
1221 be of much use to you.)\fP
1223 The general format of a tcp protocol line is:
1227 \fIsrc > dst: flags data-seqno ack window urgent options\fP
1231 \fISrc\fP and \fIdst\fP are the source and destination IP
1232 addresses and ports.
1233 \fIFlags\fP are some combination of S (SYN),
1234 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
1235 \fIData-seqno\fP describes the portion of sequence space covered
1236 by the data in this packet (see example below).
1237 \fIAck\fP is sequence number of the next data expected the other
1238 direction on this connection.
1239 \fIWindow\fP is the number of bytes of receive buffer space available
1240 the other direction on this connection.
1241 \fIUrg\fP indicates there is `urgent' data in the packet.
1242 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
1244 \fISrc, dst\fP and \fIflags\fP are always present.
1246 depend on the contents of the packet's tcp protocol header and
1247 are output only if appropriate.
1249 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1254 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1255 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1256 rtsg.1023 > csam.login: . ack 1 win 4096
1257 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1258 csam.login > rtsg.1023: . ack 2 win 4096
1259 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1260 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1261 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1262 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1266 The first line says that tcp port 1023 on rtsg sent a packet
1269 The \fBS\fP indicates that the \fISYN\fP flag was set.
1270 The packet sequence number was 768512 and it contained no data.
1271 (The notation is `first:last(nbytes)' which means `sequence
1273 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1274 There was no piggy-backed ack, the available receive window was 4096
1275 bytes and there was a max-segment-size option requesting an mss of
1278 Csam replies with a similar packet except it includes a piggy-backed
1280 Rtsg then acks csam's SYN.
1283 The packet contained no data so there is no data sequence number.
1284 Note that the ack sequence
1285 number is a small integer (1).
1286 The first time \fItcpdump\fP sees a
1287 tcp `conversation', it prints the sequence number from the packet.
1288 On subsequent packets of the conversation, the difference between
1289 the current packet's sequence number and this initial sequence number
1291 This means that sequence numbers after the
1292 first can be interpreted
1293 as relative byte positions in the conversation's data stream (with the
1294 first data byte each direction being `1').
1295 `-S' will override this
1296 feature, causing the original sequence numbers to be output.
1298 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1299 in the rtsg \(-> csam side of the conversation).
1300 The PUSH flag is set in the packet.
1301 On the 7th line, csam says it's received data sent by rtsg up to
1302 but not including byte 21.
1303 Most of this data is apparently sitting in the
1304 socket buffer since csam's receive window has gotten 19 bytes smaller.
1305 Csam also sends one byte of data to rtsg in this packet.
1306 On the 8th and 9th lines,
1307 csam sends two bytes of urgent, pushed data to rtsg.
1309 If the snapshot was small enough that \fItcpdump\fP didn't capture
1310 the full TCP header, it interprets as much of the header as it can
1311 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1313 If the header contains a bogus option (one with a length
1314 that's either too small or beyond the end of the header), \fItcpdump\fP
1315 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1316 options (since it's impossible to tell where they start).
1318 length indicates options are present but the IP datagram length is not
1319 long enough for the options to actually be there, \fItcpdump\fP reports
1320 it as ``[\fIbad hdr length\fP]''.
1322 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1324 There are 8 bits in the control bits section of the TCP header:
1326 .I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN
1328 Let's assume that we want to watch packets used in establishing
1330 Recall that TCP uses a 3-way handshake protocol
1331 when it initializes a new connection; the connection sequence with
1332 regard to the TCP control bits is
1338 2) Recipient responds with SYN, ACK
1344 Now we're interested in capturing packets that have only the
1345 SYN bit set (Step 1).
1346 Note that we don't want packets from step 2
1347 (SYN-ACK), just a plain initial SYN.
1348 What we need is a correct filter
1349 expression for \fItcpdump\fP.
1351 Recall the structure of a TCP header without options:
1355 -----------------------------------------------------------------
1356 | source port | destination port |
1357 -----------------------------------------------------------------
1359 -----------------------------------------------------------------
1360 | acknowledgment number |
1361 -----------------------------------------------------------------
1362 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1363 -----------------------------------------------------------------
1364 | TCP checksum | urgent pointer |
1365 -----------------------------------------------------------------
1368 A TCP header usually holds 20 octets of data, unless options are
1370 The first line of the graph contains octets 0 - 3, the
1371 second line shows octets 4 - 7 etc.
1373 Starting to count with 0, the relevant TCP control bits are contained
1378 ----------------|---------------|---------------|----------------
1379 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1380 ----------------|---------------|---------------|----------------
1381 | | 13th octet | | |
1384 Let's have a closer look at octet no. 13:
1394 These are the TCP control bits we are interested
1396 We have numbered the bits in this octet from 0 to 7, right to
1397 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1399 Recall that we want to capture packets with only SYN set.
1400 Let's see what happens to octet 13 if a TCP datagram arrives
1401 with the SYN bit set in its header:
1412 control bits section we see that only bit number 1 (SYN) is set.
1414 Assuming that octet number 13 is an 8-bit unsigned integer in
1415 network byte order, the binary value of this octet is
1419 and its decimal representation is
1423 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1426 We're almost done, because now we know that if only SYN is set,
1427 the value of the 13th octet in the TCP header, when interpreted
1428 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1430 This relationship can be expressed as
1436 We can use this expression as the filter for \fItcpdump\fP in order
1437 to watch packets which have only SYN set:
1440 tcpdump -i xl0 tcp[13] == 2
1443 The expression says "let the 13th octet of a TCP datagram have
1444 the decimal value 2", which is exactly what we want.
1446 Now, let's assume that we need to capture SYN packets, but we
1447 don't care if ACK or any other TCP control bit is set at the
1449 Let's see what happens to octet 13 when a TCP datagram
1450 with SYN-ACK set arrives:
1460 Now bits 1 and 4 are set in the 13th octet.
1466 which translates to decimal
1470 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1473 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1474 expression, because that would select only those packets that have
1475 SYN-ACK set, but not those with only SYN set.
1476 Remember that we don't care
1477 if ACK or any other control bit is set as long as SYN is set.
1479 In order to achieve our goal, we need to logically AND the
1480 binary value of octet 13 with some other value to preserve
1482 We know that we want SYN to be set in any case,
1483 so we'll logically AND the value in the 13th octet with
1484 the binary value of a SYN:
1488 00010010 SYN-ACK 00000010 SYN
1489 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1491 = 00000010 = 00000010
1494 We see that this AND operation delivers the same result
1495 regardless whether ACK or another TCP control bit is set.
1496 The decimal representation of the AND value as well as
1497 the result of this operation is 2 (binary 00000010),
1498 so we know that for packets with SYN set the following
1499 relation must hold true:
1501 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1503 This points us to the \fItcpdump\fP filter expression
1506 tcpdump -i xl0 'tcp[13] & 2 == 2'
1509 Note that you should use single quotes or a backslash
1510 in the expression to hide the AND ('&') special character
1516 UDP format is illustrated by this rwho packet:
1520 \f(CWactinide.who > broadcast.who: udp 84\fP
1524 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1525 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1527 The packet contained 84 bytes of user data.
1529 Some UDP services are recognized (from the source or destination
1530 port number) and the higher level protocol information printed.
1531 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1532 RPC calls (RFC-1050) to NFS.
1534 UDP Name Server Requests
1536 \fI(N.B.:The following description assumes familiarity with
1537 the Domain Service protocol described in RFC-1035.
1538 If you are not familiar
1539 with the protocol, the following description will appear to be written
1542 Name server requests are formatted as
1546 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1548 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1552 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1553 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1554 The query id was `3'.
1555 The `+' indicates the \fIrecursion desired\fP flag
1557 The query length was 37 bytes, not including the UDP and
1558 IP protocol headers.
1559 The query operation was the normal one, \fIQuery\fP,
1560 so the op field was omitted.
1561 If the op had been anything else, it would
1562 have been printed between the `3' and the `+'.
1563 Similarly, the qclass was the normal one,
1564 \fIC_IN\fP, and omitted.
1565 Any other qclass would have been printed
1566 immediately after the `A'.
1568 A few anomalies are checked and may result in extra fields enclosed in
1569 square brackets: If a query contains an answer, authority records or
1570 additional records section,
1575 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1576 is the appropriate count.
1577 If any of the response bits are set (AA, RA or rcode) or any of the
1578 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1579 is printed, where \fIx\fP is the hex value of header bytes two and three.
1581 UDP Name Server Responses
1583 Name server responses are formatted as
1587 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1589 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1590 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1594 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1595 with 3 answer records, 3 name server records and 7 additional records.
1596 The first answer record is type A (address) and its data is internet
1597 address 128.32.137.3.
1598 The total size of the response was 273 bytes,
1599 excluding UDP and IP headers.
1600 The op (Query) and response code
1601 (NoError) were omitted, as was the class (C_IN) of the A record.
1603 In the second example, \fIhelios\fP responds to query 2 with a
1604 response code of non-existent domain (NXDomain) with no answers,
1605 one name server and no authority records.
1606 The `*' indicates that
1607 the \fIauthoritative answer\fP bit was set.
1609 answers, no type, class or data were printed.
1611 Other flag characters that might appear are `\-' (recursion available,
1612 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1614 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1617 Note that name server requests and responses tend to be large and the
1618 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1620 Use the \fB\-s\fP flag to increase the snaplen if you
1621 need to seriously investigate name server traffic.
1623 has worked well for me.
1628 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1629 on UDP/137, UDP/138 and TCP/139.
1630 Some primitive decoding of IPX and
1631 NetBEUI SMB data is also done.
1633 By default a fairly minimal decode is done, with a much more detailed
1634 decode done if -v is used.
1635 Be warned that with -v a single SMB packet
1636 may take up a page or more, so only use -v if you really want all the
1639 If you are decoding SMB sessions containing unicode strings then you
1640 may wish to set the environment variable USE_UNICODE to 1.
1642 auto-detect unicode srings would be welcome.
1644 For information on SMB packet formats and what all te fields mean see
1645 www.cifs.org or the pub/samba/specs/ directory on your favourite
1646 samba.org mirror site.
1647 The SMB patches were written by Andrew Tridgell
1651 NFS Requests and Replies
1653 Sun NFS (Network File System) requests and replies are printed as:
1657 \fIsrc.xid > dst.nfs: len op args\fP
1658 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1661 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1662 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1663 sushi.201b > wrl.nfs:
1664 144 lookup fh 9,74/4096.6878 "xcolors"
1665 wrl.nfs > sushi.201b:
1666 reply ok 128 lookup fh 9,74/4134.3150
1671 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1672 to \fIwrl\fP (note that the number following the src host is a
1673 transaction id, \fInot\fP the source port).
1674 The request was 112 bytes,
1675 excluding the UDP and IP headers.
1676 The operation was a \fIreadlink\fP
1677 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1678 (If one is lucky, as in this case, the file handle can be interpreted
1679 as a major,minor device number pair, followed by the inode number and
1681 \fIWrl\fP replies `ok' with the contents of the link.
1683 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1684 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1685 Note that the data printed
1686 depends on the operation type.
1687 The format is intended to be self
1688 explanatory if read in conjunction with
1689 an NFS protocol spec.
1691 If the \-v (verbose) flag is given, additional information is printed.
1697 sushi.1372a > wrl.nfs:
1698 148 read fh 21,11/12.195 8192 bytes @ 24576
1699 wrl.nfs > sushi.1372a:
1700 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1705 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1706 which have been omitted from this example.) In the first line,
1707 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1708 at byte offset 24576.
1709 \fIWrl\fP replies `ok'; the packet shown on the
1710 second line is the first fragment of the reply, and hence is only 1472
1711 bytes long (the other bytes will follow in subsequent fragments, but
1712 these fragments do not have NFS or even UDP headers and so might not be
1713 printed, depending on the filter expression used).
1714 Because the \-v flag
1715 is given, some of the file attributes (which are returned in addition
1716 to the file data) are printed: the file type (``REG'', for regular file),
1717 the file mode (in octal), the uid and gid, and the file size.
1719 If the \-v flag is given more than once, even more details are printed.
1721 Note that NFS requests are very large and much of the detail won't be printed
1722 unless \fIsnaplen\fP is increased.
1723 Try using `\fB\-s 192\fP' to watch
1726 NFS reply packets do not explicitly identify the RPC operation.
1728 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1729 replies using the transaction ID.
1730 If a reply does not closely follow the
1731 corresponding request, it might not be parsable.
1733 AFS Requests and Replies
1735 Transarc AFS (Andrew File System) requests and replies are printed
1741 \fIsrc.sport > dst.dport: rx packet-type\fP
1742 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1743 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1746 elvis.7001 > pike.afsfs:
1747 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1748 new fid 536876964/1/1 ".newsrc"
1749 pike.afsfs > elvis.7001: rx data fs reply rename
1754 In the first line, host elvis sends a RX packet to pike.
1756 a RX data packet to the fs (fileserver) service, and is the start of
1758 The RPC call was a rename, with the old directory file id
1759 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1760 file id of 536876964/1/1 and a new filename of `.newsrc'.
1762 responds with a RPC reply to the rename call (which was successful, because
1763 it was a data packet and not an abort packet).
1765 In general, all AFS RPCs are decoded at least by RPC call name.
1767 AFS RPCs have at least some of the arguments decoded (generally only
1768 the `interesting' arguments, for some definition of interesting).
1770 The format is intended to be self-describing, but it will probably
1771 not be useful to people who are not familiar with the workings of
1774 If the -v (verbose) flag is given twice, acknowledgement packets and
1775 additional header information is printed, such as the the RX call ID,
1776 call number, sequence number, serial number, and the RX packet flags.
1778 If the -v flag is given twice, additional information is printed,
1779 such as the the RX call ID, serial number, and the RX packet flags.
1780 The MTU negotiation information is also printed from RX ack packets.
1782 If the -v flag is given three times, the security index and service id
1785 Error codes are printed for abort packets, with the exception of Ubik
1786 beacon packets (because abort packets are used to signify a yes vote
1787 for the Ubik protocol).
1789 Note that AFS requests are very large and many of the arguments won't
1790 be printed unless \fIsnaplen\fP is increased.
1791 Try using `\fB-s 256\fP'
1792 to watch AFS traffic.
1794 AFS reply packets do not explicitly identify the RPC operation.
1796 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1797 replies using the call number and service ID.
1798 If a reply does not closely
1800 corresponding request, it might not be parsable.
1803 KIP Appletalk (DDP in UDP)
1805 Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1806 and dumped as DDP packets (i.e., all the UDP header information is
1810 is used to translate appletalk net and node numbers to names.
1811 Lines in this file have the form
1823 The first two lines give the names of appletalk networks.
1825 line gives the name of a particular host (a host is distinguished
1826 from a net by the 3rd octet in the number \-
1827 a net number \fImust\fP have two octets and a host number \fImust\fP
1828 have three octets.) The number and name should be separated by
1829 whitespace (blanks or tabs).
1832 file may contain blank lines or comment lines (lines starting with
1835 Appletalk addresses are printed in the form
1841 \f(CW144.1.209.2 > icsd-net.112.220
1842 office.2 > icsd-net.112.220
1843 jssmag.149.235 > icsd-net.2\fR
1849 doesn't exist or doesn't contain an entry for some appletalk
1850 host/net number, addresses are printed in numeric form.)
1851 In the first example, NBP (DDP port 2) on net 144.1 node 209
1852 is sending to whatever is listening on port 220 of net icsd node 112.
1853 The second line is the same except the full name of the source node
1854 is known (`office').
1855 The third line is a send from port 235 on
1856 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1857 the broadcast address (255) is indicated by a net name with no host
1858 number \- for this reason it's a good idea to keep node names and
1859 net names distinct in /etc/atalk.names).
1861 NBP (name binding protocol) and ATP (Appletalk transaction protocol)
1862 packets have their contents interpreted.
1863 Other protocols just dump
1864 the protocol name (or number if no name is registered for the
1865 protocol) and packet size.
1867 \fBNBP packets\fP are formatted like the following examples:
1871 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1872 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1873 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
1877 The first line is a name lookup request for laserwriters sent by net icsd host
1878 112 and broadcast on net jssmag.
1879 The nbp id for the lookup is 190.
1880 The second line shows a reply for this request (note that it has the
1881 same id) from host jssmag.209 saying that it has a laserwriter
1882 resource named "RM1140" registered on port 250.
1884 another reply to the same request saying host techpit has laserwriter
1885 "techpit" registered on port 186.
1887 \fBATP packet\fP formatting is demonstrated by the following example:
1891 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1892 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1893 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1894 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1895 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1896 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1897 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1898 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1899 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1900 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1901 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1902 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1903 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1904 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
1908 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1909 up to 8 packets (the `<0-7>').
1910 The hex number at the end of the line
1911 is the value of the `userdata' field in the request.
1913 Helios responds with 8 512-byte packets.
1914 The `:digit' following the
1915 transaction id gives the packet sequence number in the transaction
1916 and the number in parens is the amount of data in the packet,
1917 excluding the atp header.
1918 The `*' on packet 7 indicates that the
1921 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
1923 resends them then jssmag.209 releases the transaction.
1925 jssmag.209 initiates the next request.
1926 The `*' on the request
1927 indicates that XO (`exactly once') was \fInot\fP set.
1932 Fragmented Internet datagrams are printed as
1936 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
1937 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
1941 (The first form indicates there are more fragments.
1943 indicates this is the last fragment.)
1945 \fIId\fP is the fragment id.
1946 \fISize\fP is the fragment
1947 size (in bytes) excluding the IP header.
1948 \fIOffset\fP is this
1949 fragment's offset (in bytes) in the original datagram.
1951 The fragment information is output for each fragment.
1953 fragment contains the higher level protocol header and the frag
1954 info is printed after the protocol info.
1956 after the first contain no higher level protocol header and the
1957 frag info is printed after the source and destination addresses.
1958 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
1959 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
1963 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
1964 arizona > rtsg: (frag 595a:204@328)
1965 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
1969 There are a couple of things to note here: First, addresses in the
1970 2nd line don't include port numbers.
1971 This is because the TCP
1972 protocol information is all in the first fragment and we have no idea
1973 what the port or sequence numbers are when we print the later fragments.
1974 Second, the tcp sequence information in the first line is printed as if there
1975 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
1976 the first frag and 204 in the second).
1977 If you are looking for holes
1978 in the sequence space or trying to match up acks
1979 with packets, this can fool you.
1981 A packet with the IP \fIdon't fragment\fP flag is marked with a
1982 trailing \fB(DF)\fP.
1986 By default, all output lines are preceded by a timestamp.
1988 is the current clock time in the form
1994 and is as accurate as the kernel's clock.
1995 The timestamp reflects the time the kernel first saw the packet.
1997 is made to account for the time lag between when the
1998 ethernet interface removed the packet from the wire and when the kernel
1999 serviced the `new packet' interrupt.
2001 traffic(1C), nit(4P), bpf(4), pcap(3)
2003 The original authors are:
2007 Steven McCanne, all of the
2008 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
2010 It is currently being maintained by tcpdump.org.
2012 The current version is available via http:
2015 .I http://www.tcpdump.org/
2018 The original distribution is available via anonymous ftp:
2021 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
2024 IPv6/IPsec support is added by WIDE/KAME project.
2025 This program uses Eric Young's SSLeay library, under specific configuration.
2027 Please send problems, bugs, questions, desirable enhancements, etc. to:
2030 tcpdump-workers@tcpdump.org
2033 Please send source code contributions, etc. to:
2039 NIT doesn't let you watch your own outbound traffic, BPF will.
2040 We recommend that you use the latter.
2042 On Linux systems with 2.0[.x] kernels:
2044 packets on the loopback device will be seen twice;
2046 packet filtering cannot be done in the kernel, so that all packets must
2047 be copied from the kernel in order to be filtered in user mode;
2049 all of a packet, not just the part that's within the snapshot length,
2050 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
2051 asked to copy only part of a packet to userland, will not report the
2052 true length of the packet; this would cause most IP packets to get an
2056 capturing on some PPP devices won't work correctly.
2058 We recommend that you upgrade to a 2.2 or later kernel.
2060 Some attempt should be made to reassemble IP fragments or, at least
2061 to compute the right length for the higher level protocol.
2063 Name server inverse queries are not dumped correctly: the (empty)
2064 question section is printed rather than real query in the answer
2066 Some believe that inverse queries are themselves a bug and
2067 prefer to fix the program generating them rather than \fItcpdump\fP.
2069 A packet trace that crosses a daylight savings time change will give
2070 skewed time stamps (the time change is ignored).
2072 Filter expressions on fields other than those in Token Ring headers will
2073 not correctly handle source-routed Token Ring packets.
2075 Filter expressions on fields other than those in 802.11 headers will not
2076 correctly handle 802.11 data packets with both To DS and From DS set.
2079 should chase header chain, but at this moment it does not.
2080 .BR "ip6 protochain"
2081 is supplied for this behavior.
2083 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
2084 does not work against IPv6 packets.
2085 It only looks at IPv4 packets.
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